Crossed slot scanner for developing a lissajous scanning pattern



United States Patent O 3,322,953 CROSSED SLOT SCANNER FOR DEVELOPING ALISSAJOUS SCANNING PATTERN Jacob S. Zuckerbraun, New York, N.Y.,assignor to Kollsman Instrument Corporation, Elmhurst, N.Y., acorporation of New York Filed Dec. l1, 1961, Ser. No. 158,335 1 Claim.(Cl. Z50-203) This invention relates to a novel reed scanning system forlight trackers, and more specifically relates to the simultaneoustwo-axes scanning for scanning in both azimuth and altitude with asingle scanning mechanism.

Scanning mechanisms of the type to which the invention is directed areset forth, for example, in my copending application Ser. No. 47,837,filed Aug. 8, 1960, now Patent Number 3,244,886, entitled LightModulation System (K-102), which is assigned to the assignee of thepresent invention.

In such scanning systems, since it is necessary to scan the light imageof a remote light source in both azimuth and altitude to obtain theposition of the image, a first scanning mechanism is arranged to scanthe light image in a first direction, and a second mechanism which isindependent from the first mechanism scans in a direction perpendicularto the scanning of the first.

With this system, and even though the two mechanisms are provided, onlyone can work at any one time so that the remote light source isalternately tracked in azimuth and in altitude, Thus, where the twomechanisms provide crossed slots which define an aperture, the firstslot is first oscillated to define a moving opening which scans thelight source in the first direction, and this is then stopped and theother slot oscillated to define a moving opening which is perpendicularor at an angle to the original motion.

Where it is desired to simultaneously scan in both directions, it hasbeen proposed to split the light image into two separate images whichare each operated upon by their own respective scanning means which scanperpendicularly with respect to one another and with respect to the twoimages. Such mechanisms are set forth in my copending application Ser.No. 77,198, filed Dec. 20, 1960, now abandoned, entitled Scanning DeviceFor Light Tracking Systems (K-105), and assigned to the assignee of thepresent invention.

In accordance with the present invention, I have found that I canprovide crossed slots in respective plates which are oscillatedperpendicularly to one another. By oscillating the first plate at afirst frequency and the second plate at a second frequency, I have foundthat the modulated light which passes through the aperture defined bythe intersection of the two slots carries information therein to bothazimuth and altitude, which information can be removed from the lightsignal and used to control the positioning apparatus of the trackingmechanism.

Accordingly, a primary object of this invention is to provide a noveltwo-axes reed scanner which continually tracks the image of a radiantbody.

Another object of this invention is to provide two slits which areperpendicular to one another for a scanning mechanism wherein the twoslits are oscillated perpendicularly to one another and at differentfrequencies.

Another object of this invention is to provide a light scanningmechanism which is simple in construction.

.A further object of this invention is to provide a novel scanningmechanism for light tracking devices which has few movable parts and ishighly reliable.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings, inwhich:

3,322,953 Patented May 30, 1967 ICC FIGURE l schematically illustratesthe telescope to be used with the novel scanning mechanism of theinvention.

FIGURE 2 illustrates a novel crossed aperture arrangement of the presentinvention.

FIGURE 3 illustrates the characteristic of various measured parameterswhen the apertures of FIGURE 2 are oscillated at different frequencies.

As pointed out above, the concept of the present invention is tooscillate cross slots in the light scanning mechanism at differentfrequencies. An analysis of the output light in such an arrangement isas follows:

Consider a star image of si) lumens focused in the plane of a single,vibrating-slot aperture. The signals developed can be described by thefollowing equation:

f0(x)=D.C. component, which is an even function of x f1(x)=fundamentalcoefiicient f2(x) :second harmonic coefficient x==displacement of starimage from null measured along the x axis.

If this modulated light is now passed through a second identical slotvibrating in the same plane, but at right angles to the first, theresultant output signals will be given by:

cos 2wyi+sum and difference terms] The scan frequencies wx and my (orfrequency of vibration of the two crossed slots respectively) are chosento be non-integral multiples of each other in order to keep sum anddifference terms outside the passbands of followup amplifiers.

The significant fiux components that reach a photosensing device areidentified as follows:

d f0()') 'f1(x) sin wxr=x axis position signal i5/0(y) f2(x) cos 2wxt=xaxis recognition signal f0(x) -f1( v) sin wyf=y axis position signal l1)0(x)f1(y) cos 2wyt=y axis recognition signal The equation for fo(x) orf0(y) is given by- A=excursion amplitude of the slots and W=slot width Aplot of this term is shown in FIGURE 3, where it can be seen that f0(x)is at least 0.5 in the range If this technique of modulation is comparedto that of the beam splitter method of my above noted application Ser.No. 77,198, now abandoned, (K-) for telescopes of the same objectivelens diameter, it can be readily seen that over the above ranges for xand y the position and recognition signals are essentially the same inboth methods. An additional important advantage to the new method isthat the noise power caused by the star at null will be one-half thevalue obtained with the beam splitter method. The new method also holdsthe same noise advantage over a rotary scanner of the type set forth inU.S. Patent 2,905,828.

One manner in which the above concepts can be embodied in a physicalconstruction is shown in FIGURES 1 and 2. FIGURE 1 illustrates atelescope 1 having an objective 2 which focuses the light rays (whichare so labeled) from a remote radiant body toward the scanning mechanism3 which is contained within telescope housing 1.

After operation on these light rays by the scanning mechanism, as willlater be described, the resultant output signals pass through a lenssystem 4 which focuses the output light on a photo-sensing device 5.

The photo-sensing device 5 generates an output which is amplified byamplifier 6. Appropriate amplifiers and tilters 7 and 8 then receive thex axis position signal and y axis position signal, by, for example,being responsive only to frequencies wx and wy respectively, and theiroutputs are then delivered to demodulator means 9 and 10 respectively,which are synchronous demodulators. Thus demodulator 9 receives starsignal frequency wx and a fixed reference of the same frequency` whiledemodulator 10 receives star signal wy and a xed reference of wy. Thedemodulators 9 and l0 then deliver appropriate correction signals to theservo system 1l which controls the position of telescope 1 and attemptsto retain the telescope pointed directly at the light source beingtracked.

The scanning mechanism 3 is shown in FIGURE 2 as including a first andsecond magnetic reed 40 and 41 which are mounted on fixed supports 42and 43 within the telescope housing 1. Each of the thin reeds 40 and 41mount thin plates 44 and 45 which have slits 46 and 47 therein. Theslits 46 and 47 are perpendicular to one another, as illustrated, sothat they define a square-shaped aperture at their intersection.

The plate 44 and its aperture 46 are oscillated by means of a magneticdrive system which includes the solenoid drive 48. while reel 41 and itsplate 45 is oscillated by the solenoid drive system 49.

In accordance with the invention, the solenoid 48 has its terminals 50and 51 connected to an A.C. source of frequency wx. The solenoid 49 hasits terminals 52 and 53 connected to a source of power having afrequency wy. Thus, the plate 44 will oscillate at a frequency wx whileplate 45 will oscillate at frequency wy. Hence, since these frequenciesare different from one another, the

square aperture defined by the intersection of slits 46 and 47 willdescribe a Lissajous figure and modulate the image of the light sourcebeing tracked in accordance with the equations set forth above.

Although this invention has been described with respect to its preferredembodiments it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of this invention be limited not bythe specific disclosure herein but only by the appended claims.

What is claimed is:

A scanning system for a light tracking device; said light trackingdevice including a telescope for forming the image of a light source tobe tracked, means for scanning the image of said light source,photosensing means positioned to receive the scanned image of said lightsource, and servo means connected between the output of saidphotosensing means and said telescope to retain said telescope pointedat said light source; said scanning means including an aperture movablewith respect to said image of said light source; said aperture beingmoved in a Lissajous scanning pattern whereby signal information forboth azimuth and altitude of said light source is continuously producedin said photosensitive means; said scanning means includng a pair ofcrossed slots movable perpendicular to one another; the first slot ofsaid pair of crossed slots moved at a first frequency; the second slotof said pair of crossed slots moved at a second frequency distinct fromsaid first frequency; said first and second slots moving with simpleharmonic motion.

References Cited UNITED STATES PATENTS 1,951.666 3/1934 Martin Z50-232 X2.000.948 5/1935 Hayes Z50-232 X 2,398,552 4/1946 Norton 250-2352,923.202 2/1960 Trimble 250-203 X 2,931,910 4/1960 Ostergren et alZ50-203 2,941,081 6/1960 Greenlee et al. Z50-203 3,011,061 ll/196lDickinson 250-237 3,083,611 4/1963 Ziolkowski 88--1 FOREIGN PATENTS616.676 3/1961 Canada. 494,667 10/1938 Great Britain.

RALPH G. NILSON, Primary Examiner.

WALTER STOLWEIN, Examiner.

CHESTER L. JUSTUS, J. D. WALL, E. STRICKLAND,

Assistant Examiners.

